Temperature controller



TEMPERATURE CONTROLLER William F. Brown, in, Bay Village, and Melvin H. Jones, (Plmsted Falls, Ohio Uriginal application December 20, 1954, Serial No. 43 036125 newdlagen No. l2,837,915, dated June 10,

W] e an tis ap ication Decemb 12 Serial No. 627,961 p er A956 2 Claims. (Cl. 219-20) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a temperature control c rcu t andmore particularly to a temperature control ClI'Culi particularly adapted to provide accurate and dependable control of the temperature of a specimen furnace of the type employed in creep and rupture testing machines.

This application is a division of application Serial No. 476,612, filed December 20, 1954, for Axial Loading Creep and Rupture Machine now Patent No. 2,837,915.

An object of the present invention is the provision of a temperature control circuit to provide accurate and dependable control of the temperature of a furnace.

Another object of the present invention is to provide a control circuit of the character described particularly adapted to control the temperature of a specimen furnace of the type employed in creep and rupture testing ma chines.

Other objects and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

The figure is a partly diagrammatic and partly schematic circuit diagram of an illustrative embodiment of the present invention.

The electric furnace control circuit shown in the figure consists essentially of a commercial temperature controller 11, such as the Celectray instrument, which senses the temperature of a furnace, such as a specimen furnace (not shown) which would in use be connected to furnace receptacle 12, an auto transformer 13 to supply a variable voltage to furnace receptacle 12 (the selection of a suitable voltage being dependent upon the desired specimen temperature), a resistor 14 normally connected in series with furnace receptacle 12 but which may be shunted by the action of temperature controller 11, and various control switches, relays, indicating instruments and receptacles therefor, and indicating lamps. The Celectray indicating instrument 11 in the applicants system could be replaced with many commercially available temperature control devices providing their sensitivity is at least i-l F. and the output is sufficient to actuate relay. A description of the instrument is given in the Weston Electrical Instrument Corp. Tag Catalogue No. 1101].

A main switch 16 is provided to control the power to all units except a maintenance receptacle 17 permanently connected across the A. C. line 18, 19 by conductors 21, 22. When switch 16 and a micro switch 23, controlled by the specimen testing apparatus, a 139th i operating winding of a mercury relay 24 1s energlzed to close the contacts thereof and power is supplied to the circuit. This condition is indicated by the lighting of. a

lamp 26.

Auto transformer 13 is connected to the phase conductor 18 by the contacts of switch 16 and relay 24, fuse 27, and conductor 28 and to the neutral conductor 19 by conductors 29, 22. One socket of furnace receptacle 12 13 connected to auto transformer 13 by conductor 29 and the other socket thereof by a series circuit comprising conductor 31, the normally closed contacts of a pushbutton switch 32, conductor 33, resistor 14, conductor 34, the contacts of a manually operable switch 36, and conductor 37.

When the furnace reaches a predetermined temperature, controller 11 is operable to complete a circuit between terminals C and L thereof to connect the operating Winding of a mercury relay 38 across the A. C. line through a circuit comprising the contacts of switch 16 and mercury relay 24, fuse 39, conductor 41, terminals C, L, conductors 42 and 22. Energization of mercury relay 38 causes the closure of the contacts thereof to complete a shunt circuit across resistor 14 comprising conductor 43, the contacts of mercury relay 38 and conductor 44. A lamp 46 is provided to indicate the shunt-- ing of resistor 14.

A running time meter 47 is connected to the A. C. line by a circuit including the contacts of switch 16 and mercury relay 24, a fuse 48, the contacts of a manually operable switch 49 and conductors S1, 22.

Receptacle 52 is provided to permit measurement of the furnace voltage and current, the furnace voltage appearing across the lower and the left sockets of receptacle 52 while the furnace current may be measured between the lower and right sockets of receptacle 52 when pushbutton switch 32 is depressed to its lower position.

The described circuit is placed into operation by closing switch 16 to energize relay 24. When bringing a cold furnace up to temperature, switch 36 and the circuit of resistor 14 may be opened. The variable transformer may then be set to give a large current flow through the furnace, thereby permitting rapid attainment of the de sired temperature. With switch 36 open, the power is either completely on or completely off during the control cycle and negligible overshooting will occur. However, were switch 36 to be left'open and the temperature of the furnace to be controlled solely by relay 38, severe undershooting and undesirably large temperature oscillations would occur. Connecting resistor 14 in series with the furnace during the off cycle largely eliminates temperature oscillations. When the desired temperature is attained, switch 36 may be closed and the variable transformer voltage reduced to a value which permits normal control action. If, thereafter, the furnace temperature drops below the desired value, controller 11 operates to close relay 38 to by-pass resistor 14 and provide full power to the furnace. When the test specimen breaks, a portion of the testing apparatus (for example lever 22 of the testing machine shown in Fig. l of Patent No. 2,337,915 referred to above) operates to open micro switch 23 (designated 79 in the above referenced patent) to deenergize mercury relay 24 thereby shutting off power to the entire circuit excepting maintenance receptacle 17. Running time meter 47, which indicates time in tenths of an hour, is started by means of switch 49 when the test cycle begins and is shut off through the action of mercury relay 24 when the specimen breaks.

The control circuit shown and described is arranged to permit control of the furnace temperature within plus or minus 3 F. with line voltage variations up to control of the furnace temperature within plus or mlnus 1 F. with constant line voltage, and control of the temperature by turning all or a preselected portion of the power to the furnace on or 011. In addition, the use of mercury relays in the temperature control circuit eliminates theproblems'caused'by contact burning or Sticking which would result were mechanical relaysemployed. Fuses 27, 39, and 48 maybe respectively valued at 20 amps., 3 amps., and 1 amp., and resistor 14 may be rated at 5 ohms, 200 watts,'and 6 amps.

Obviouslymany-modifications and variations of the presentinventionare possiblein'the light of't'ne above teachings. It is therefore to be understood that'within the scope of the appended claims;the invention'rnay be practiced otherwise than as specifically described.

What is claimed-is:

1. An electric furnace temperature control circuit for use with anaxialloading creep and rupture machine, comprising: a first mercury relay, a variabletransformer furnace, and switch means connected in circuit with said resistor'and'operabletoopenthe circuit 'of the same whereby operation of the =temperature controller causes the power to the furnace to be all on or all oh.

2. A temperature control circuit for controlling the temperature of a specimen'fu'rnace' comprising: a transformer having theprimary winding thereof connected to a source of power, a furnace connected in series with a resistortothesecondary winding of said transformer, a

temperature controller operative when said furnace reaches aipredetermined temperature to shunt said resistor, manually operable circuit breaking means connected inser-ies withsaid resistor, andmeans operative to deenergize the entire control circuit when the specimen breaks.

References Cited in thefileof this patent UNITED STATES PATENTS 2,479,319 Crowley et al. Aug. 16, 1949 2,546,926 Hart Mar. 27, 1951 2,602,916 Anderson July 8, 1952 2,752,473 Hage June 26, 1956 

